The protection of crops against insects has involved the use of organic synthesis products with a wide spectrum of action which are intended to kill insects in a non-specific manner. The amounts required are large. Many of these products are hazardous to the environment and some, such as DDT, have been banned.
Insects may also be controlled by chemical mediators which regulate insect-insect relationships or plant-insect relationships. Among such chemical mediators are pheromones, kairomones, and allomones. Pheromones are chemical substances that are use for communication between individual organisms of the same species. Allomones cause a reaction in another species which is favorable to the organism secreting the substance. Kairomones are either nonadaptive or detrimental to the organisms producing them.
In contrast with conventional products for the destruction of insects, these mediators are used in very low amounts, for example two or three treatments of 10 to 20 grams per hectare, or continuous diffusion of a few milligrains per hectare and per hour for one or more months.
U.S. Pat. No. 4,734,281 describes a method for diffusing insect sex pheromones into the air. These pheromones modify behavior by preventing the reproduction of certain insects. These pheromones, which are in liquid form, are placed in polyethylene bags. The pheromones diffuse through the bag and become dispersed into the air. Example 1 of the patent shows polyethylene tubes 0.8 mm in internal diameter, 1.4 mm in outside diameter, and 200 mm in length that are filled with 80 mg of a mixture of two pheromones. The ends of the tubes are then sealed. At 30.degree. C. in a stream of air of 0.5 m/s, a diffusion of 0.4 and 0.5 mg per day of each pheromone is observed.
U.S. Pat. No. 5,142,817 describes sheets or strips formed of a sheet of water-insoluble polymer adhesively bonded to a sheet of a hydrophilic matrix. This matrix may be made of cellulose fibers, polyester, polyacetate, polyvinyl alcohol, or polyoxyethylene glycol. This matrix contains a plasticizer such as polyoxyethylene glycol or a sorbitol solution and also a biologically active product. These strips serve to envelop trees. The biologically active product is released by a humid atmosphere and serves to protect the trees.
EP 367,140 describes copolymers of ethylene and of vinyl acetate containing 5 to 30% of p-menthane-3,8-diol, an insect repellent. Granules may be made therefrom, which are placed on the roots of trees or on the collars of domestic animals.
Japanese Application 87 JP-069396, published as KOKAI JP 63238001, describes strips for winding around the branches of trees, consisting of a photodegradable sheet covered with a mixture of an insecticide and a polyether urethane or polyester urethane prepolymer.
Japanese Application 81 JP-024042, published as KOKAI JP 57 139005, describes compositions of pheromones and of a binder containing 4 to 20% of pheromones. The binder is silicone or SBR rubber. A solvent such as methylene chloride, benzene, an alcohol, etc. and fillers such as cellulose, silica, active carbon, or carbonate are also used. The product is in paste form.
Patent FR 2,579,983 describes perfume-filled polymers which diffuse these perfumes into the ambient air.
The prior art shows the diffusion of liquid pheromones through polyethylene containers. The preparation of these polyethylene tubes, their filling with pheromones, the sealing and then the transportation and the positioning in the crops is complicated.
The diffusion of pheromones from pastes filled with between 4 and 20% of pheromones requires the transportation and the positioning of considerable amounts of fillers. In addition, the diffusion from a paste is not as uniform as the diffusion of a liquid through a wall.